Journal
JOURNAL OF APPLIED PHYSIOLOGY
Volume 105, Issue 2, Pages 742-748Publisher
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/japplphysiol.01256.2007
Keywords
adults; substrate utilization; indirect calorimetry; fat metabolism; cycling
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The range of exercise intensities that elicit high fat oxidation rates (FOR) in youth and the influence of pubertal status on peak FOR are unknown. In a longitudinal design, we compared FOR over a range of exercise intensities in a small cohort of developing prepubertal male subjects. Five boys all at Tanner stage 1 (ages 11 - 12 yr) and nine men (ages 20 - 26 yr) underwent an incremental cycle ergometry test to volitional exhaustion. FOR curves were determined from indirect calorimetry during the final 30 s of each increment. The same protocol was duplicated annually in the boys as they progressed through puberty. The peak FOR was considerably higher (P < 0.05) in boys at Tanner 1 (8.6 +/- 1.5 mg.kg lean body mass(-1).min(-1)) (mean +/- SD) compared with men (4.2 +/- 1.1 mg.kg lean body mass(-1).min(-1)). FOR dropped as boys developed through puberty (Tanner 2/ 3 peak rate = 7.6 +/- 0.6 mg.kg lean body mass(-1).min(-1); Tanner 4 peak rate = 5.4 +/- 1.8 mg.kg lean body mass(-1).min(-1), main effect of Tanner stage; P < 0.05) to the levels found in men (not significant). The exercise intensity that elicited peak FOR was higher in the boys at Tanner 1 [56 +/- 6% peak aerobic power ((V) over dot(O2) peak)] than in men (31 +/- 4% (V) over dot(O2) peak) (P < 0.001). This value tended to decrease by Tanner stage 4 (45 +/- 10% (V) over dot(O2) peak, main effect of Tanner stage; P = 0.06). We conclude that, compared with men, prepubertal boys have higher relative FOR throughout a wide range of exercise intensities and that FOR drops as boys develop through puberty.
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